It is estimated that 46.2 million adults use both nicotine and alcohol with 6.2 million reporting a comorbid alcohol use disorder and nicotine dependence [1]. While it is known that nicotine's addictive properties are mediated by activation of nicotinic acetylcholine receptors (nAChRs) within the dopaminergic (DAergic) brain areas associated with reward [2], it is unclear how ethanol modulates its rewarding properties. Recent studies have suggested that ethanol, like nicotine, activates nAChRs within the mesolimbic reward pathway [3], however, because of the diversity of nAChR subunits expressed within the brain's DAergic reward pathway, an important goal of alcohol research is identifying which of these subunits most directly modulates ethanol reinforcement. Previous research has shown that nAChR containing the alpha-4 subunit (a4*) are critical for nicotine reward, tolerance and dependence [4]. This proposal will investigate the hypothesis that a4* nAChRs modulate voluntary ethanol drinking, ethanol preference and reward. To address this, I will use a combination of mouse genetics, behavioral assays, pharmacology and viral gene re-expression. Two complementary nAChR mouse models will be used in this proposal, one that does not express high affinity a4* nAChRs and another that expresses hypersensitive a4* nAChRs. These mice will be used in a limited access self-administration assay called Drinking in the Dark (DID) in which mice voluntarily drink ethanol to the point of intoxication [5]. In AIM 1, I will examine the role of the a4* nAChRs in ethanol voluntary drinking by combine the nAChR mouse models with pharmacology in the DID assay. In AIM 2 I will explore the role of a4* nAChRs in ethanol preference and reward using a modified DID assay and conditioned place preference. In AIM 3 I will test the hypothesis that a4* nAChRs within the VTA are sufficient for ethanol voluntary drinking by re-expressing the a4 subunit using an adeno-associated viral expression vector. The anticipated results from these experiments will yield valuable insight into the biology of alcohol dependence as well as identify potential targets for alcohol cessation therapeutics. Nicotine, the primary addictive component of tobacco smoke, and alcohol are the two most widely co- abused drugs in the world suggesting that they may activate the same reward pathway in the brain. The goal of this proposed project is to better understand the molecular mechanisms that contribute to the use of nicotine and alcohol, the two most commonly co-abused drugs in the world. Insights gained from this project should help identify molecular targets for alcohol cessation therapeutics.